Classic Threads . . . on the virtues of vacuum systems

March 2002

We were discussing the relative merits of vacuum systems versus
electrical systems and whether or not one was being foolish
by choosing to put all his/her instrumentation eggs in the one
electrical basket.
One reader cited a case where a pilot flew a single engine airplane
into convective conditions, took a strike. As with all dark
and stormy night stories with happy endings, this one had its
hero . . . a vacuum system that continued to power gyros after
the electrical system was toast.
This anecdote was offered as compelling data in favor
of retaining the electrical independence of vacuum systems. We'll
pick up the thread here where I am questioning the value of
the data cited. Why would one go off to do research and development
in an environment KNOWN to be a strike risk with an electrical
system NOT proven to be resistant to strike stresses . . .

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The key phrase here was in the second paragraph: " . . .
PURPOSELY flown for the past several summers into developing
vertical clouds as a part of R & D." Why anyone would do that
in this kind of airplane is beyond my comprehension. We've all
seen the 4-engine, turbo-prop airplanes they fly into
hurricanes on the Weather Channel. I've seen numerous programs
on aircraft versus nature studies where pilots went into
thunder storms WANTING to take a strike.
Bob,
I have to disagree. That the pilot PURPOSELY flew into clouds is, in my
opinion, not relevant in the least. Is a lightning strike from clouds I
flew into on purpose any different from a lightning strike from clouds I
inadvertently flew into?
How is it not relevant? When I write up a plan to do
anything out of the ordinary in the way of flight testing,
lots of people take an intense interest in what I'm asking
both pilot and airplane to do. Just a few months ago, I wanted
to mount a new laser altimeter in a flight test Bonanza and
get performance at 15-100 feet off the water over some large, local
lakes. Got shot down because the safety folks didn't want to
take an airplane that close to the water and a long way off
shore . . . now, if I'd consider moving the experiment to
a twin turboprop . . . my test budget wouldn't accommodate
the change of machines.
I think anyone that chooses to go into convective conditions
(I presume he was on an IFR flight plan and got weather
briefings) when the airplane is not equipped to deal with
conditions that are KNOWN to reside there, the pilot is
multiplying his risk by several orders of magnitude .
In the case cited, he DID have vacuum gyros and the day
ended on a happy note. I presume his safety committee deemed the
action to be relatively low risk and his experiences
bore out that assessment . . . I am truly happy for
him . . . I don't think my safety committee would
have bought into it.
How is the experience you cited relevant to our discussion? How do
we know that if he'd been equipped with a modern electrical
system with multiple power sources for electric gyros that
his day would have ended any differently? Bowing at the
altar of vacuum systems based on anecdotal information is
not good engineering. Flying into stormy conditions in a poorly
equipped aircraft is not good piloting.
I have never found it difficult to avoid flying into
convective activity and I don't plan on needing that
protection in the future. If there are builders who
embrace the same operating philosophy for their airplane,
my assertion is that there's no reason for them
to enjoy "benefits" of vacuum systems while being
deprived of the benefits of all-electric systems.
Are electronics designed to protect against inadvertent lightning strikes
but not purposeful ones?
Of course not . . .
What DIFFERENCE does it make whether the pilot purposefully flew into clouds
or not? The original poster had a very valid point that, in your prejudice
against vacuum systems, you ignored using this rather flimsy argument. A
lightning strike is much more likely to affect electrical systems than
vacuum systems.
The difference was he wanted to be there and took pains to make
it happen. He took the hit and survived. For myself and I believe
for most builders, we take pains not to be there and probability
of taking the hit is very close to zero.
We all know your prejudice, Bob, and you have given a
series of consistent and well thought out arguments for your favor of
electrical systems over vacuum systems.
Prejudice . . . ???? Really? Let's see. Webster says:
1 : injury or damage resulting from some judgment or action of another
in disregard of one's rights; especially : detriment to one's legal rights
or claims
Nope. Nothing here.
2 a (1) : preconceived judgment or opinion (2) : an adverse opinion or
leaning formed without just grounds or before sufficient knowledge b :
an instance of such judgment or opinion c : an irrational attitude of
hostility directed against an individual, a group, a race, or their
supposed characteristics
Preconceived? No, post-conceived based analysis and observations
of field history for a technology that has not materially improved
for over 5 decades while the alternative technologies have steadily
advanced.
" . . . without just ground or before sufficient knowledge."
Again, I don't think so . . .been working this stuff successfully
for too many years to have ignored the facts and physics of
the two technologies.
But you can't completely dismiss the benefits of a vacuum system, and your
attempts to do so with arguments like this simply undermine your
credibility. I wonder: if someone comes up with a REAL good argument in
favor of vacuum systems, are you going to be grown up enough to admit
someone else might have a better idea than you?
Never have dismissed the benefits of vacuum systems. They were
absolutely fantastic in 1950 . . . they allowed us to go off
and do things in weather with reasonable confidence that the
flight would not end badly. But, that technology has been static
while electronics continues to improve.
Bob, you're a tremendously valuable resource to the homebuilder community.
I've learned a lot here that will find its way into my aircraft. But your
overt bias leads me to question everything you say is a bad idea, because
I'm never sure if it's a bad idea for logical reasons, or because you don't
like it and are trying to justify your bias to us with meaningless argument.
Bias? I admit to being ENTHUSIASTIC about electrical/electronic
solutions to problems but I object to being labeled
as "biased" . . . just a few days ago I worked hard
to talk a guy out of doing an elaborate electronic
flap control system in favor of a more ELEGANT, failure
resistant mechanical system.
Which of my assertions is meaningless? Here are my assertions
about vacuum systems: They have a high cost of ownership;
they're bulky, heavy, and require a lot of maintenance
compared to their electrical counterparts. Every time I've
had to pull a panel down loaded with vacuum instruments, I had
to take time and extra-ordinary care to make sure open hoses didn't
take a contaminant . . . I then had to worry about getting
everything tight when it went back in while trying to swing
a wrench in a space dominated with a bunch of hoses.
In this instance, I think that purposely flying into clouds is a meaningless
argument. (The rest of your post might have contained factual information,
but none of it addressed the original issue: "With all the drawbacks of
vacuum systems... it still kept working when all the electron powered stuff
quit.")
I'd hoped that my line of reasoning was founded
on how most of us operate our airplanes where lighting
avoidance is a high priority thereby making the argument
on those grounds moot.
For example: do you plan to have any form of de-icing
on your airplane? Hot prop? Boots? Wet wing? If not, why
not? Do you plan to have radar? How about a ballistic
recovery parachute? (Hmmm . . . I wonder if anyone has considered
adding air-bags to their cockpit equipment installations.)
As I mentioned in the post, none of our big airplanes have
vacuum systems and they get struck regularly. If one is truly
concerned about lightning susceptibility in a light aircraft
then by all means, have a vacuum system. Personally, I'd find
little comfort for having a vacuum system in my airplane if
there were strikes going on all around me and the gyros were
the ONLY system on board with any demonstrated degree of
strike resistance.
If a builder has reasonable and considered confidence that
he can maintain separation from conditions where lightning
is a hazard, then why suffer the premiums for an "insurance
policy" that literally sucks while adding little if any value?
The decision to add any kind of risk mitigation system
your airplane has to be weighed against the magnitude
of that risk. How you plan to use the airplane is a major
component of risk calculation. To extol what may be the
only virtue of a vacuum system (resistance to lightning
strike) makes no sense unless you also make the
effort to shield yourself against OTHER hazards to be
found in the same clouds. In spite of the fact that
many of the airplanes I fly around in are tested for
survival in these extremes, I appreciate the fact that
pilots I ride with work diligently to stay the hell out
of such conditions . . .
These questions (and others like them) require answers by
the guy building the airplane with consideration
as to how HE and the AIRPLANE are going to operate.
Only then can one deduce what equipment configuration
makes sense for convenience of operation AND risk
mitigation when things begin to go badly.
I've oft decried the reverence with which we repeat
dark-and-stormy-nights stories and run off to arm
ourselves against the same scenario without understanding
how the event came to pass (so that we can avoid it)
and knowing what tools are available to help us out
instead of reacting in classic and perhaps ill-considered
ways.
Bob . . .